FIG. 1 is a simplified block diagram schematically representing a typical prior art network router 10. Packet forwarding router 10 includes two major subsystems: control plane 12 and data plane 11. Data plane 11 provides the packet forwarding function in interfaces 14 for store-and-forward transit packets. This subsystem relies on a packet forwarding “look-up” table that is created and maintained by control plane 12. The forwarding table instructs data plane 11 where to forward each received packet. Control plane 12 creates the packet forwarding table using information from various sources, including static configuration and dynamic information learned from peer network routers through connections 15-1 through 15-N and interfaces 14, and communicates the forwarding tables to interfaces 14.
In prior art systems, command line interface (CLI) 13 is a text-based system associated with control plane 12 for applying configuration changes to a router's operational state. The router's operational state at any particular time can be queried and displayed as the set of text-based configuration commands that would place a newly started router with no operational state into its current operational state. CLI 13 also provides the ability to execute a sequence of text-based configuration commands. For example:                ip activate-fsdm        router jsam 22        peer 1.2.3.4        end        tcp enable-wdsm(Note that in this and following examples fsdm and wsdm are artificial commands solely for the purpose of illustrating the configuration rollback process.)        
Text-based configuration commands have a “positive” form (a command that activates a particular operational state attribute) and a “negative” form (a command that turns off a particular operational state attribute). The “negative” form of the configuration command is written as the positive form of the command with the keyword “no” prepended to the text. For example:                (positive-form) “ip activate-fsdm”        (negative-form) “no ip activate-fsdm”        
CLI 13 also has commands within its command structure belonging to particular configuration “levels”. A configuration level is entered by execution of a “level-command” in CLI 13. After entering a configuration level, a user obtains access to “level-specific-commands” associated with that specific level. A configuration level is exited by executing a level-exit command to enter an operational state, known as “base-command-level,” from which the user either can enter another configuration level or can access a set of base-level configuration commands directly without entering another level. For example:                (level-command) routerjsam 22        (level-specific-command) peer 1.2.3.4        (level-exit-command) end        
Prior art routers are typically configured using a configuration file. To roll back the configuration, in other words to move the router from one configuration in time with one set of operating parameters to another by issuing a single command involved an internal database. To accomplish the rollback required completely reinitializing the router in most respects and reprocessing all of the configuration commands, in effect wiping the slate clean of the current configuration, and then rolling back to the previous configuration.
Prior art solutions are very complex and very difficult to implement, intrusive into software, and very cumbersome to maintain correctly over time. Nevertheless, many users liked the configuration rollback feature on routers. Historically, in the telecommunication industry, the ability to roll back quickly to a previous configuration appears, for example, on PBXs and telephone equipment in some form, but not in a form specifically applicable for routers.
It would therefore be desirable to wipe this slate clean without the router ceasing to operate, thereby eliminating everything that the router currently knows about it's configuration and putting something new in its place, without damaging or interrupting the router in its current operation.
Almost every installed router has a running configuration file of some sort. Accordingly, it would be desirable to provide a configuration rollback process compatible with a large population base of installed routers, that does not require rebooting or interrupting the router or its connections with peer network routers.